Dave and Lynn Waller are no millionaires. In 1992, they bought a historic firehouse in Malden, Mass., for $32,500. Today, the Mountain Avenue property is worth far more. The Wallers decided the maximum amount they could borrow against it was their limit in their bid to buy the Graves Island Light Station from the federal government.

In the end, that amount turned out to be enough. The couple bought the wind- and wave-swept lighthouse at the edge of Boston Harbor for $933,888. Reached by phone today, Waller described how he transferred the money to the U.S. General Services Administration from his phone yesterday evening, while on board a boat on the harbor. He was on an impulse diving excursion near The Graves, the rocky outcropping on which the lighthouse stands.

If that sounds like the style of a yacthing millionaire, Waller probably doesn't fit the bill. For one thing, he doesn't actually own a boat. Trips he's taken out to The Graves have been on board small charters like the one he took with Boston SCUBA out of East Boston, yesterday.

He's the owner of a video effects company based on Newbury Street in Boston. Brickyard VFX has 22 employees and has counted Acura, New Balance and Cumberland Farms among its clients. Funny thing, Dave Waller said – he and Lynn mortgaged their house to start Brickyard VFX, too.

"What it's worth is what two people (bidders) are willing to pay for it," Waller said, describing his trepidation as a bidding war shaped up between himself and another, as-yet unknown bidder for the lighthouse. "We don't have a million dollars in the bank. We were bidding against people that had lots of millions of dollars in the bank."

The Wallers' home is assessed at $437,000. As a historic firehouse it might be a tricky one to assess accurately - so maybe it is worth the near million dollars the Wallers paid for the lighthouse.

But according to Waller, his identity was widely known – among a small group of people. When he joined the dive cruise Thursday, the operator of the boat asked him right away if he was the guy who bought the lighthouse.

"I went what the [expletive], I haven't even bought it yet, how did you know?"

Correction: An earlier version of this story mis-stated the name of the dive charter company that brought Waller out to The Graves. It was Boston SCUBA.